Fig. 4. Effects of Alx1 MOs in S. purpuratus (A-H) and L. variegatus (I-P). MOs were complementary to non-overlapping regions of the Spalx1 and Lvalx1 mRNAs and produced essentially identical phenotypes in the two species. Control embryos show normal PMC ingression (A,I, arrows), PMC migration (B,J, arrows), and skeletogenesis (C,D,K,L, arrows). Alx1 MO-injected embryos lacked PMCs (E,M) and invaginated in a delayed fashion (F,N, arrows). They failed to form skeletal elements even after prolonged culture (H,P). Eventually they developed a tripartite gut (H,P, arrows), pigment cells (see Fig. 5), blastocoelar cells, and coelomic pouches (P, arrowhead). Ectodermal territories appear to differentiate normally (thickened oral ectoderm is indicated by the arrow in G and the double arrow in P). Arrow in O indicates expanded archenteron tip in L. variegatus embryos injected with Alx1 MO.

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